1. Field of the Invention
The present invention generally relates to stereophonic sound processing systems for localizing a sound image at a desired location in the ambience of a listener and, more particularly, to a stereophonic sound processing system comprising a plurality of stereophonic filter means having different processing capabilities and performance so that one of the plurality of stereophonic filter means is selected as required.
Recently, with an increasing use of multimedia, the number of personal computers equipped with audio output is increasing. Associated with this, a large number of multimedia products such as games are produced, providing stereophonic sound when such a product is run on a personal computer. As the performance of a CPU and the like is rapidly improving, it has become possible to generate stereophonic sound in response to an operation of a user. There is a need for a stereophonic sound processing system capable of appropriately performing a stereophonic sound process so as to enable the user to enjoy the image and the associated stereophonic sound simultaneously without the user being aware of a drop in the processing speed.
It is also to be noted that an increasing number of multimedia products are created using a personal computer. Accordingly, there is a need for a system that can efficiently produce stereophonic sound using a personal computer.
2. Description of the Related Art
FIG. 1 shows a principle of a stereophonic sound process. For example, a microphone is attached to both ears of a dummy head 2 located in an anechoic room so as to pick up sound from a sound source 1. A transfer function Sly between a sound source in a desired orientation and a left ear, and a transfer function Sr. between the same sound source and a right ear are obtained using a setup as illustrated in FIG. 1. In reproduction, an input signal from a sound source 3 is processed using processing devices 4 and 5 provided with the transfer functions Sly and Sr., respectively, so that a user can hear stereophonic sound. A process is also needed for canceling characteristics of an output device such as a headphone or a speaker. More specifically, the characteristics of a headphone or a speaker are canceled using a processing device 6 (Hxe2x88x921).
FIG. 2 is a graph showing a transfer function measured between a sound source 30xc2x0 displaced to the front left of a listener and a left ear of the listener, using a setup as shown in FIG. 1. FIG. 3 is a graph showing a frequency characteristic of the transfer function of FIG. 2. FIG. 4 is a block diagram showing how the transfer function of FIG. 2 is represented by a finite impulse response (FIR) filter or a infinite impulse response (IIR) filter normally having a total of several hundred taps. Cancellation of the characteristics of the output device is also implemented by a filter. In other words, the processing devices 4, 5 and 6 are implemented by a FIR filter or an IIR filter.
FIG. 5 is a block diagram showing a construction of a stereophonic sound processing system according to the related art. Transfer functions that correspond to a variety of locations of a sound source are obtained using a setup as shown in FIG. 1. In generating stereophonic sound, an input signal is processed using the transfer function that corresponds to the localization of a sound image. More specifically, a filter factor to be applied to a filter 12 is selected by a filter factor selection unit 11 depending on the localization of the sound image. The filter factor selection unit 11 may refer to a filter table storing filter factors that correspond to different orientations of the sound source. FIG. 6 shows such a filter table. For example, the table may contain a filter factor that corresponds to the transfer function occurring when the sound source is located to the front of the listener, a filter factor that corresponds to the transfer function occurring when the sound source is located 30xc2x0 to the left of the listener, . . . a filter factor that corresponds to the transfer function occurring when the sound source is located 30xc2x0 to the right of the listener, etc.
FIG. 7 is a flowchart showing an operation of the stereophonic sound processing system according to the related art. In step ST1, the stereophonic sound processing system reads a signal from a sound source. In step ST2, localization of the sound source is read. In step ST3-1, a filter factor that corresponds to the localization is selected by referring to the filter table. In step ST3-2, a filter process is executed. In step ST4, the signal subjected to the filter process is output as stereophonic data, thus completing the stereophonic sound process.
As shown in FIG. 5, the stereophonic sound processing system according to the related art is provided with a sound source and localization of a sound image. The stereophonic sound processing system then subjects the input signal to a stereophonic sound process so as to output stereophonic data. The stereophonic sound process requires a filter having a total of several hundred taps so that dedicated hardware is normally used. In an ordinary personal computer, a general-purpose CPU is used to execute the stereophonic sound process. The dedicated hardware is characterized by high performance and large processing volume. The personal computer is characterized by low processing volume and slightly poor quality of localization due to a simpler process. The dedicated hardware is available as a high-end product for professionals and the software process is commercialized as personal-use software.
Thanks to the recent improvement in CPU performance, it has become possible to implement a high-precision stereophonic sound process only by software. More specifically, it has become easy to perform a high-precision stereophonic sound process by running applications intended for multimedia production on a personal computer as well as on a workstation or a large-scale computer. While high-precision stereophonic sound may be preferable in some types of usage and applications, it may be preferable to produce not so high-precision stereophonic sound in other types of usage and applications. For example, a producer of a stereophonic sound product may be required to produce predetermined stereophonic sound in a given period of time, irrespective of the performance of a CPU. In other words, the processing volume may have to be reduced. In such a case, efficient stereophonic sound production is possible by sacrificing the precision so that the processing time is maintained constant. While a stereophonic sound production system has been hitherto limited to either a high-precision specification or a low-precision specification, it is desirable that advantages of both specifications can be selected on a case-by-case basis.
In another aspect, it is of course desirable that high-precision stereophonic sound and low-precision stereophonic sound can be appropriately selected so as to satisfy an end user enjoying stereophonic sound by running an interactive application such a game on a personal computer.
Accordingly, a general object of the present invention is to provide a stereophonic sound processing system in which the aforementioned desired improvements are made.
Another and more specific object is to provide a stereophonic sound processing system for reproducing stereophonic sound using a personal computer adapted for multimedia such that stereophonic sound most appropriate for the performance of a processing device used in the personal computer and for the requirement of a user is generated. It is to be appreciated that, with the present invention, a production application or an end-user application can be compatible with both high-precision stereophonic sound and low-precision stereophonic sound.
The aforementioned objects can be achieved by a stereophonic sound processing system for localizing sound image at desired locations using devices including a headphone and a speaker, comprising processing means for generating stereophonic sound on the basis of an input signal; said processing means further comprising: a plurality of stereophonic filter means each comprising an FIR filter for processing an input signal; selecting means for selecting one of said plurality of stereophonic filter means in accordance with a desired factor; wherein said processing means controls the selected stereophonic filter means so as to generate stereophonic sound on the basis of a processed result supplied by the selected stereophonic filter means.
The aforementioned objects can also be achieved by a computer-readable recording medium storing a stereophonic sound processing program for localizing sound image at desired locations using devices including a headphone and a speaker, said stereophonic sound processing program comprising processing means for generating stereophonic sound on the basis of an input signal; said processing means further comprising: a plurality of stereophonic filter means each comprising one of an FIR filter and an IIR filter for processing an input signal; selecting means for selecting one of said plurality of stereophonic filter means in accordance with a desired factor; wherein said processing means controls the selected stereophonic filter means so as to generate stereophonic sound on the basis of a processed result supplied by the selected stereophonic filter means.
According to the present invention, stereophonic sound can be produced in accordance with requirements of a producer of the stereophonic sound or an end user.